The invention relates to rotary drilling, and more particularly, to steered directional drilling with a rotary drilling tool.
In the earth drilling art, it is well known to use downhole motors to rotate drill bits on the end of a non-rotating drill string. With the increasingly common use of directional drilling, where the well is drilled in an arc to produce a deliberately deviated well, bent subs have been developed for guiding the downhole motors in a desired drilling direction. The bent subs are angled, and thus cannot be used in association with rotating drill strings.
This invention is directed towards a tool that permits steered directional drilling with a rotary drilling tool.
The device contemplated provides a method for positioning the drill bit in a drilling operation to achieve small changes in hole angle or azimuth as drilling proceeds. Two different positions are available to the operator. The first is a straight ahead position where the tool essentially becomes a packed hole stabilizer assembly. The second position tilts the bit across a rotating fulcrum to give a calculated offset at the bit-formation interface. The direction that the bit offset is applied in relation to current hole direction is controlled by positioning the orienting pistons prior to each drilling cycle, through the use of current measurement-while-drilling (MWD) technology.
In one aspect of the invention, components of the tool comprise a MWD housing, upper steering and drive mandrel, non-rotating position housing, lower drive mandrel splined with the upper mandrel, rotating fulcrum stabilizer and drill bit.
If, after surveying and orienting during a connection, it is desired to drill with the tool in the oriented position, the rig pumps are activated. The pressure differential created by the bit jets below the tool will cause pistons to open from the ID of the tool into the tool chamber. As the pistons open, they will contact wings that come out into the path of travel of the upper mandrel as it comes down a spline, and bottoms out on the lower drive mandrel. This occurs as the drill string is being lowered to bottom. The extra length provided by the open wings moves a sliding sleeve centered over, but not attached to the upper mandrel, to a new position that in turn forces the orienting pistons to extend out into the borehole annulus. This extrusion pushes the non-rotating sleeve (outer housing) to the opposite side of the hole. When this force is applied across the rotating stabilizer, the stabilizer becomes a fulcrum point, and forces the drill bit against the side of the hole that is lined up with the orienting pistons. The calculated offset at the bit then tends to force the hole in the oriented direction as drilling proceeds. After the drilling cycle is complete, the tool will be picked up off bottom, and as the upper mandrel moves upward on the spline in the lower mandrel, a spring pushes the sliding sleeve back into its normal position, the orienting pistons retract into the outer housing, and the centering pistons come back out into the borehole annulus, thus returning the tool to its normal stabilized position. This cycle may be repeated until the desired result is achieved.
Once the desired hole angle and azimuth are achieved, the following procedure may be implemented to drill straight ahead. After making a connection and surveying, slowly lower the drill string to bottom and set a small amount of weight on the bit. Then engage the rig pumps. This time, when the activation pistons from the ID attempt to open the wings, they will be behind the sliding sleeve assembly, and the sliding sleeve will remain in its normal or centered position throughout the following drilling cycle.
Skillful alternating of the two above drilling positions will yield a borehole of minimum tortuosity, when compared to conventional steerable methods.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.